Systems may control the engine in a vehicle based on the vehicle mass and inclination. For example, the engine output torque, wheel torque, or other operating parameters may be more accurately controlled to match driver requests when the vehicle mass and/or inclination can be estimated, measured, and/or otherwise identified.
One approach to identify vehicle mass and/or vehicle inclination is applicable in a four wheeled vehicle where only two wheels are driven. Specifically, un-driven wheel velocities are measured and used to determine, along with other parameters, the vehicles longitudinal velocity, longitudinal acceleration, mass, and inclination.
However, the inventors herein have recognized a potential disadvantage with such an approach. For example, in a vehicle with four-wheel drive, the torque applied to each wheels may cause a loss of traction on any and all wheels. Thus, the wheel velocities may not correlate with the vehicles longitudinal acceleration under selected conditions.
In another approach, one or more accelerometers may be used to identify vehicle mass and/or vehicle inclination. Again, the inventors have recognized a potential disadvantage with such an approach. In particular, the accelerometer sensor may degrade and/or may provide erroneous readings under selected conditions.
To address at least some of these issues, in one embodiment, a method of operating a vehicle having at least a driven wheel, may be used. The method may comprise maintaining an inclination angle of the vehicle in memory during a vehicle off condition; after starting the vehicle from the vehicle off condition, first updating a vehicle mass based on operating conditions including vehicle traveling conditions; and after updating the vehicle mass, updating the inclination angle based on operating parameters including vehicle traveling conditions.
In this way, it is possible to take advantage of the fact that in most circumstances, the surface inclination will not change when the vehicle is stopped (assuming it is not transported), and that the vehicle mass is most likely to change when the vehicle is stopped. Not only that, but the vehicle mass is further most likely not to change while the vehicle is moving, especially in the case of passenger vehicles and trucks. As such, improved estimates may be obtained, even without data from a longitudinal acceleration sensor.
In another embodiment, a method of operating a vehicle is provided having at least a driven wheel, the driven wheel driven at least by a driving torque, may be used. The method may comprise: during a first mode where the vehicle operates with the wheel driven and with reduced slip and where wheel speed response correlates to driving torque, updating at least one of vehicle inclination and mass during the first mode based on an operating parameter, and during a second mode where the vehicle operates with the wheel driven and with increased slip and where wheel speed response is un-correlated to driving torque, maintaining a previous value for at least one of inclination and vehicle mass. Further, when updating vehicle inclination and vehicle mass, an initial inclination from previous vehicle operation may first be used so that a new vehicle mass can be determined, and then after learning the vehicle mass, the inclination can again be updated.
In this way, both engine torque control and traction control may be improved. For example, it may be possible to identify vehicle inclination or mass with sufficient accuracy during non-slipping conditions, while avoiding inaccurate readings during slipping conditions. Likewise, it may be possible to accurately diagnose a degraded accelerometer sensor, even in 4×4 vehicles that may experience periodic slipping conditions.
In one particular example, improved operation may be achieved in a vehicle that selectively transfers torque from back to front wheels, of vice versa, responsive to slip, in coordination with engine-torque-reduction based traction control. When torque is primarily provided to one set of driving wheels, a second set of wheels may be used to estimate vehicle mass and/or inclination. However, during a slipping condition where traction control may intervene with driver requested torque, and where torque may be at least partially transferred and delivered to the second set of wheel via a transfer case, previous values of the inclination and/or mass may be used. In this way, even in 4×4 type vehicles, improved performance may be achieved.